Methods of producing oil-free and wax-free surfaces on polyurethane moldings

ABSTRACT

1. A PROCESS FOR PRODUCING POLYURETHANE MOLDINGS HAVING SURFACES FREE OF ADHESION INHIBITING MOLD RELEASE AGENT COMPRISING THE STEPS OF: (A) OVERCOATING A MOLD, WHICH HAS BEEN COATED WITH A HYDROPHOBIC MOLD-RELEASE AGENT, WITH A CONTINUOUS, SOLID BARRIER LAYER OF A WATER-SOLUBLE FILM FORMING (b) PASSING INTO THE MOLD A POLYURETHANE MOLDING (B) PASSING INTO THE MOLD A POLYURETHANE MOLDING COMPOSITION CONTAINING REACTIVE ISOCYANATE GROUPS, (C) POLYMERIZING SAID POLURETHANE MOLDING COMPOSITION IN CONTACT WITH SAID BARRIER LAYER MATERIAL CONTAINING A PLURALITY OF MOIETIES REACTIVE WITH ISOCYANATE GROUPS, (D) REMOVING THE RESULTANT MOLDING, AND (E) WASHING THE SURFACE OF SAID MOLDING WITH WATER TO SUBSTANTIALLY REMOVE SAID WATER-SOLUBLE BARRIER LAYER.

United States" Patent US. Cl. 26446.4 9 Claims ABSTRACT OF THEDISCLOSURE Polyurethane moldings are made by methods using a mold whichhas been coated with a hydrophobic oily or waxy release agent andovercoated with a film forming water-soluble barrier material (e.g.polyvinyl alcohol) which is reactive with the free isocyanate materialsof the molding composition. The moldings are washed to remove thewater-soluble barrier material to provide a surface free of oily or waxyresidue.

DISCLOSURE This application is a continuation in part of our copendingpatent application, Ser. No. 881,926, filed Dec. 3, 1969 and nowabandoned.

This invention relates to a method of producing paintable surfaces onpolyurethane moldings. Specifically, this invention relates to themethod of preparing moldings with release agents so that a moldinghaving surfaces which are clean, blemish-free, and free of adhesioninhibiting mold release agent, suitable for painting, will result.

Polyurethane moldings, especially foamed polyurethane moldings, areuseful in a broad variety of applications. For many uses, it isdesirable to subsequently coat or paint the surface of the molding witha decorative or protective layer. conventionally, these layers areapplied to a polyurethane molding, by means of brushing, spraying andother methods known in the art, paint-like compositions commonly knownto the art. Typically, in the prior art methods, the polyurethanemolding is prepared in a mold which is first coated with an oily, waxyfluororganic, or silicone release agent. The release agent serves thepurpose of allowing easy removal of the molding from the mold surfacesand providing a smooth and uniform surface to the molding. A problemarises, however, when these polyurethane moldings are subsequentlypainted because the waxy or oily release agent often leaves a film onthe surface of the molding which may be undetectable to the touch or theeye but which will prevent the adhesion of a paint or coating layer. Thepaint or coating layer may, as a consequence, blister, flake, or peelfrom the surface of the molded article. To alleviate this problem, ithas been common in the art to submit the molding to subsequent stepswhich were designed to remove from the surface of the molding the oilyor waxy residue of the release agent used in the mold. Means such asroughening the surface of the molding with an abrasive material andcleaning the surface of the molding with an abrasive material andcleaning the surface of the molding with a solvent which will solubilizethe oily or waxy residue, have been used. These methods have not beengenerally satisfactory and have the further disadvantage of costlinessand often adversely alter the surface of the molding.

ICE

Where conventional release agents are used to coat the mold; theproblems of poor release, surface blemishes, and undesirable residues ofthe release agent on the molding are encountered.

The economical manufacture of molded polyurethane especially foamedpolyurethane articles having surfaces which are satisfactory forpainting, has, therefore, been difficult by methods known in the priorart. The release agents are necessary to allow the removal of moldingsfrom the mold and yet their use causes the aforementioned problems. Amethod has now been discovered by which polyurethane moldings havingsurfaces free of adhesion inhibiting mold release agent, and havingsmooth oiland wax-free, paintable surfaces are obtained and importantlyalso, which may be easily released from the mold.

It is, therefore an object of this invention to overcome thedisadvantages of the prior art and to provide a method for themanufacture of molded polyurethane articles having a paintable surfaceto which paint strongly adheres.

Another object of this invention is to produce polyurethane moldingshaving surfaces that are totally oiland wax-free.

Still another object of this invention is to accomplish the productionof moldings with a paintable surface to which paint strongly adheres, inan economical and eflicient manner.

Still other objects of the present invention will be apparent from thefollowing discussion.

Briefly, this invention comprises the treatment of a conventional moldwith a waxy or oily material which may be an organic or siliconematerial and the subsequent coating of this already treated surface witha solid film forming, water-soluble, isocyanate reactive material. Whenthe resultant water-soluble barrier layer is dry, a molding is made witha polyurethane mix in the conventional manner. After molding the articleis easily re,- moved from the mold, and is washed with water, aqueousdetergent, or slightly alkaline aqueous solution. After drying, thesurface may be painted by methods known in the art and said paintedsurface shows no evidence of poor paint adhesion because of residual oilor wax spots from the release agent.

For purposes of description of this invention, the hydrophobic, oily, orwaxy coating layer first applied to the mold is designated the releaseagent. The hydrophylic water-soluble layer which is subsequentlyovercoated onto the mold is designated the barrier layer.

It has been found, according to this invention, that when a mold is usedfor consecutive moldings, as it will be in production operations forwhich this method is intended that the water-soluble barrier layer isadvan tageously applied every cycle, while the oily or waxy mold releaseagent need only be applied every three or four cycles. It is noted thatthe barrier layer adheres more tenaciously to the molded article than tothe mold (which is coated with release agent).

The adhesion of the hydrophylic barrier layer to the molded articlerather than to the mold surface and the additional use of a barrierlayer overcoated hydrophobic release agent on the mold surface providetwo important distinctions over the methods known in the prior art. Itis recognized that certain of the materials disclosed herein as thebarrier layer have been used in the prior art as mold release agents.The use of the same and similar materials herein as barrier layersrather than mold release layers is no mere semantic distinction. A moldrelease agent, as is known in the molding art, is designed to allow easyremoval of the molded article from the mold and the release agentadvantageously adheres strongly to the mold but not to the moldedarticle. In fact, as those skilled in the art would recognize, an idealrelease agent would be one which adhered so strongly to the mold thatonly single or very infrequent application would be necessary. However,it is commonly known to those skilled in the art, that films of oily orwaxy mold release agents adhere to the molded articles and are difficultto remove therefrom. In contradistinction, the materials designatedherein as barrier layers adhere to the molded article, are applied'ineach molding operation, and true mold release agents of distinctlydifferent properties are utilized in conjunction therewith. In theabsence of the waxy type mold release on the surface of the mold it isknown for the barrier'layer to adhere strongly to the mold surface aswell as to the molded polyurethane foam article thereby making removalof said article from the mold very difiicult.

' As-will be shown in the working examples, the adhesion of the barrierlayer to the molded article has been demonstrated by incorporating a dyein the barrier layer. With the barrier layers which have been utilizedin the practice of this invention, this adhesion between the barrierlayer and the molding is attributed to a chemical reaction at theinterface. These barrier layers contain a plurality of moieties whichare reactive with the free isocyanate groups of the polyurethane moldingcomposition. Thus various water-soluble, film forming organic compoundscontaining --OH, COOH, NH CONH NHR, CONHR where R is a hydrocarbylradical with 1-12 carbon atoms or other functional groups reactive withisocyanate groups can function as the barrier layer in the practice ofthis invention. It is theorized for example that when a polyhydroxymaterial such as polyvinyl alcohol is used as the barrier layer, aninterfacial reaction occurs between the hydroxy groups of the barrierlayer and the free isocyanate groups in the components of the moldingcomposition. The reaction between free isocyanate groups, which appearin polyurethane molding compositions, and polyhydroxy-containingmaterials is well-known. It is not surprising, therefore, that thisreaction should occur at the surface of the molding. It was, however,totally unexpected that the described isocyanate-reactive barrier layerswould function in this invention. It was expected that the entirethickness of the barrier layer would react with the isocyanate in themolding composition to give the same net effect of no barrier layerwhatsoever. Other barrier layer materials containing moieties known toreact with isocyanate groups and which themselves are known to bereactive with isocyanate groups would be expected to also totally reactwith the isocyanate groups of the polyurethane molding composition so asto have a net eflfect of no barrier layer. The contrary was found, and,in fact, barrier layers which are reactive are preferred in the practiceof this invention.

Examples of barrier layer materials known to react with isocyanategroups include polyacrylic acid, hydroxy methyl cellulose, polyvinylpyrrolidone, polymers of hydroxy alkyl acrylates, polymers of hydroxyalkylmethacrylates, sodium silicate, polymethacrylic acid, polyvinylalcohol and higher molecular weight polyoxyalkylene glycols (e.g.molecular weight about 10,000). Reaction of various of the abovecompounds with isocyanate groups is known in the chemical art andreported in the chemical and related literature. French Pat. 1,520,222discloses reaction of polymers and copolymers containing acid groupswith isocyanate bearing compounds. K. R. Lange, Chemical Ind. (London)1968, (14), pp. 441-3, reports the reaction of tolylene diisocyanatewith silica. The reaction of polyisocyanates with polyvinylpyrrolidinone is disclosed in US. 3,216,983. Reaction of isocyanates(e.g. tolylene diisocyanate) with polyhydroxy compounds such ascopolymers of hydroxylated esters of acrylic or methacrylic acid isdescribed in Belgium Pat. 629,937.

Disclosure is made in Belgium Pat. 630,318 as to the reaction ofpolyisocyanates with polymers and copolymers of hydroxyalkylacrylates orhydroxyalkylmethacrylates. The reaction of primary and secondary aminesand amides with isocyanates is disclosed in e.g. Polyurethane byDombrow, Reinhold Publishing Corporation, N.Y. pp. 18, 30.

The consequence of the theorized reaction between for example thehydroxy groups and isocyanate groups is that a portion of thewater-soluble barrier layer, e.g., the polyhydroxy layer, is integratedwith the surface of the molded article, and in all probability isreacted only at the interface forrned between the molding and thebarrier layer. The surface of a polyhydroxy barrier layer closest to theoily or waxy release agent apparently does not react with freeisocyanate groups because, as shown by the dye test in Example 1, thebarrier layer retains its water solubility.

Consequently, the polyhydroxy layer adheres strongly to the moldedarticle and is removed therewith when the article is taken from themold. The entire thickness of the barrier layer adhering to the moldingremains water soluble, except possibly for a reacted and insolubilizedzone at the interface of the molding and barrier layer. Therefore, thepart removed from the mold, in effect, has an outer surface easilyremovable with water, aqueous detergent, or aqueous alkali. Any of thewaxy release agent sticking to the water-soluble outer surfaces of themolding is also easily removed with the aqueous washings.

It is considered necessary, as stated above, that the water-solublebarrier layer be reactive with free isocyanate groups contained in themolding composition so that the tendency of the barrier layer to adhereto the molding itself is much greater than its tendency to adhere to thewaxy or oily mold release agent.

Among the materials useful as the barrier layer are any of thewater-soluble inorganic or organic materials capable of forming a solid,continuous layer on the release agent-coated mold. Sodium silicate is anexample of an inorganic material useful in the method of this invention.Among the organic materials, polymers are particularly preferred.Polyvinyl alcohol and hydrolyzed polyvinyl acetate polymers have beenfound to be particularly advantageous in this invention. Polyvinylalcohol is Water-soluble and is conventionally prepared by thesubstantially complete hydrolysis of polyvinyl acetate polymer.Partially hydrolyzed polyvinyl acetate polymers, especially those inwhich about of the acetate groups are hydrolyzed, are also water-solubleand operative and desirable in the process of this invention. Otherpolymeric materials which may be used include higher molecular weightpolyoxyalkylene glycols, polyvinyl pyrrolidone polymers, polyvinylmethyl ether/maleie anhydride copolymers, hydroxy methyl cellulose andwater-soluble hydroxy-substituted acrylate or methacrylate polymers orcopolymers, polyacrylic acid, polymethacrylic acid, and natural polymerssuch as gelatin, albumin, hydrolyzed starch, modified starches, and thelike. Non-polymeric organic materials which may be used as barrierlayers include sugars, rat-methyl glucoside and the like. If desired, anon-ionic hydroxyl-containing surfactant, such as octylphenoxypoly(ethyleneoxy) ethanol containing 9-10 moles ethylene oxide per mole ofhydrophobe, may be added to the solution to effect faster wetting of thewaxy release agent by the barrier layer composition.

The term water-soluble as used herein includes solubility in liquids.which are essentially aqueous, such as aqueous alkali and water-solventsystems in which Water forms the predominant part. The term does notimply that the barrier layer must be applied from water solvent.

In fact, it is preferable if the barrier material can be applied fromvolatile solvent or aqueous-solvent solutions. Rather, the termwater-soluble means that the barrier layer is easily removable from themolding by wa ter, i.e. water per se or water containing systems. Theadvantages of the ability to use water per se or aqueous solutions forthis purpose are obvious in terms of cost, non-toxicity, availabilityetc.

The mold release agent is applied directly to the mold and is ahydrophobic, oily or waxy organic or silicone material and is selectedfrom those materials which are wellknown in the molding art. A number ofproprietary compositions exist which contain as their primary ingredientorganic oils, organic waxes, silicone oils and waxes, and the like.Common materials such as paraflin, petroleum, carnauba wax, and thelike, may also be used. The invention is not dependent on the type ofhydrophobic release agent which is used. Rather the invention lies inthe conjoint use of a hydrophobic release agent and a watersolublebarrier layer.

In general, the method of this invention may be easily adapted to anypolyurethane molding process. The method is, of course, particularlyuseful where the molded part is to be subsequently painted or where awaxand oil-free surface is required or desired. In practicing thisinvention, the following series of steps have been successfully used toproduce, in a consecutive fashion, painted moldings from a single mold:

1. Apply mold release;

A. Apply hydrophobic mold release agent (every three cycles). B. Apply(water-soluble) barrier layer over mold release coating (every cycle);Assemble mold; Introduce polyurethane molding ingredients; Allowingredients to foam and to cure; Disassemble mold; Remove moldedarticle; Wash molded article with mild aqueous detergent solution, 8.Air dry; 9. Apply paint; 10. Repeat process.

The polyurethane molding compositions and methods of their preparationwhich may be utilized in the practice of this invention are compositionsand methods commonly known in the art. Said polyurethane moldingcompositions contain at least one organic polyisocyanate (i.e. anorganic compound containing at least two isocyanate groups permolecule), at least one polyol (i.e. an organic compound having at leasttwo hydroxyl groups per molecule), and optionally one or more surfaceactive agents, one or more catalysts, one or more fire retardants, oneor more light stabilizers, one or more pigments and/or fillers orreinforcements. Organic polyisocyanates commonly known to the art whichmay be employed in the polyurethane molding composition include but arenot limited to 2, 4 tolylene diisocyanate, 2,6 tolylene diisocyanate andmixtures thereof, crude tolylene diisocyanate, polyethylenepolyphenylisocyanate, 4,4 diphenylmethane diisocyanate, phenylenediisocyanate, xylylene diisocyanate, naphthylene diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate and like aliphatic,cycloaliphatic, aromatic and substituted aromatic polyisocyanates.Isocyanate terminated reaction products obtained by reacting an excessof organic polyisocyanate, such as those de scribed above, withpolyhydroxy compounds (e.g. polyvether polyols, ethylene glycol,glycerine, trimethylol propane, pentaerylthritol and like monomeric andpolymeric polymeric polyhydroxy compounds) may be used in the moldingcompositions. Polyhydroxy compounds such as, but not limited to, polyolsobtained by reacting alkylene oxides (e.g. ethylene oxide, 1,2-propyleneoxide, 2,3 butylene oxide and the like) with polyhydric alcohols (e.g.ethylene glycol, glycerol, trimethylol propane, pentaerythritol,sorbitol, sucrose or a-methyl glycoside) or alkylene diamines (e.g.ethylene diamine) may be used in the polyurethane molding compositionsemployed in the practice of this invention. Hydroxy terminatedpolyesters such as those obtained by condensation of a polycarboxylicacid (e.g. dicarboxylic acid) with a polyhydric alcohol (e.g. diol ortriol) may be used in the said polyurethane compositions. Halogenatedand/or phosphorus containing polyols may be employed in the saidpolyurethane molding compositions. Reaction products obtained byreacting glycols or alkylene oxides with dimethyl siloxane orpolydimethyl siloxane are among the more commonly known surfactantswhich may be used in the polyurethane molding composition. Catalystsusable in the said polyurethane molding compositions include but are notlimited to organo tin compounds and tin salts such as dibutyl tindilaurate and stannous octoate, tertiary amines such triethylenediamine, triethanol amine and N,N,N ,N tetramethyl-1,3-butane diamine orcombinations of said tin and amine compounds.

Blowing agents commonly known to those skilled in the art and which maybe used in the polyurethane compositions employed in the practice ofthis invention include but are not limited to water and low boilinghalogenated hydrocarbons such as monofluorotrichloromethane,dichlorodifluoromethane and trichlorotrifluoroethane. Among the fireretardants commonly known to those skilled in the art and which may beused in the said polyurethane molding compositions include halogenand/or phosphorus containing organic compounds (e.g. tris(B-chloroethyl) phosphate), antimony trioxide, ammonium phosphate andthe like. Antioxidants and ultraviolet light stabilizers well known tothe art may be added to the polyurethane molding composition. Organicand/ or inorganic pigments may be included. Fillers such as diatomaceousearth, magnesium silicate, asbestos and the like may be used in the saidpolyurethane molding compositions.

It is to be recognized that this invention does not lie in thepolyurethane molding composition and therefore many variations in themolding composition may be practiced by those skilled in the art withoutdeparting from the scope and spirit of this invention.

The invention may be better understood by reference to the followingexamples in which all parts and percentages are by weight unlessotherwise indicated.

These examples are designed to teach those skilled in the art how topractice the invention and to represent the best mode contemplated forcarrying out the present invention and are not intended to limit thescope of the invention in any manner.

EXAMPLE 1 This example illustrates the preparation of a foamedpolyurethane molding having an oiland wax-free, paintable surface. Thisexample also illustrates the adhesion of the barrier layer to themolding.

A small aluminum foil dish is coated with a Wax-type release agentcomprising a paste dispersion of wax in a hydrocarbon solvent in whichthe wax portion is a mixture of hydrocarbon and ester-type waxes, andovercoated with a proprietary composition comprising polyvinyl alcoholand a surfactant in water/ alcohol solution. A small proportion of analcohol-soluble green dye was added to the polyvinyl alcohol solution.The coating was applied by wetting the inside of the aluminum dish withthe polyvinyl alcohol solution, draining off the excess, and drying.

The polyurethane-forming ingredients used in this and subsequentexamples are as follows:

A-Component (isocyanate) A quasi-prepolymer prepared by slowly adding atambient temperature 56 lbs. of polypropylene glycol of MW about 400 to444 lbs. of a commercial isocyanate reported to be a polymer of diphenylmethane diisocyanate having 2-5 isocyanate groups per molecule. (Theingredients were mixed and allowed to react and stand for 24 hoursbefore analysis and use.)

51.6 Grams of the A-component and 48.4 grams of the B-component weremixed with a high speed propellor-agitator, and 10.7 grams of this mixwas poured into the prepared aluminum foil dish and allowed to react andexpand.

After substantially complete foaming, the dish is placed in acirculating air oven at 120 degrees F. for 20 minutes. Upon removing thedish from the oven, the molded part is removed. The molded article iseasily released and has a green coating. None of the green coating isdiscernible on the mold (dish). The green coating is easily removed bywashing the molded article with water.

EXAMPLE 2.

B-component. After the foam has expanded, the molda ing in the mold isplaced in a 120 degree F. oven for 20 minutes to cure the molding.

The resulting molding is easily removed from the mold. None of the greendye is noted on the mold. The greendyed barrier layer is easily removedby washing with water. After drying, the surface of the molding is brushpainted with an acrylic latex paint. Good adhesion and a uniform paintedsurface result.

EXAMPLE 3 This is a control example to illustrate the eifect of omissionof the mold release agent.

The procedure of Example 2 is repeated except that the mold releaseagent coating is omitted. Severe sticking of the molded part is notedand removal from the mold is difiicult. Surface blemishes are alsonoted.

EXAMPLE 4 This is a control example to illustrate the effect of omissionof the barrier layer in the method of this invention.

The procedure of Example 2 is followed, except that the polyvinylalcohol coating (barrier layer) is omitted. Non-uniformity and spotty,poor adhesion is noted in the painted article.

EXAMPLE 5 This example illustrates the use of a variety of materials as(1} the mold release agent, and as (2) the barrier layer.

The procedure of Example 2 is repeated with the ex ception that each ofthe following materials is substituted for the wax-type mold releaseagent and the polyvinyl alcohol barrier layer used in Example 2respectively.

A. Mold Release Agents 1. A suspension in a hydrocarbon solvent of ablend of paraffinic microcrystalline and chemically modified Montanwaxes having a melting point of about 140 degrees F.

. 8 A blend of vegetable, petroleum, and synthetic waxes in a solvent.3. White petroleum jelly. 4. A commercially available paste Wax. 5. Acommercially available hydrocarbon wax having the following properties:

Melting point-190 degrees F.-minimurn Penetration at 77 degrees F.--8maximum Color ASTM D1500BI'OWI1 maximum Acid No.--Nil SaponificationNil.6. Carnauba wax.

B. Barrier Layers a-Methyl glucoside.

. Sodium silicate. Partially (72.977%) hydrolyzed polyvinyl acetatecontaining 37-42% residual polyvinyl acetate on a weight basis andhaving a molecular weight of 2000'.

In each case, release of the molding from the mold is easy, and thebarrier layer is easily removed by washing with Water to give moldingscomparable in quality to those obtained in Example 2.

EXAMPLE 6 This example demonstrates (a) the interaction between aclaimed barrier layer material and a polymerizing urethane compositionin contact with said barrier layer applied over a wax (b) the generationof a polyurethane plastic surface to which paint strongly adheres, and(c) the ability to remove from the polyurethane plastic surfacesubstantially all of the barrier layer material with water to leave aWax free and oil free polyurethane plastic surface having highwettability and strong paint adhesion in a practice of this invention.

A. Casting A solution was prepared as follows:

Materials.-Polyol component:

Lb. Poly-G-43SDM 1 55.58 PolyG-560DM 2 22.96 Niax Catalyst TMBDA 3 .679DC-l93 Surfactant 4 1.602 LVT23P 5 21.18

Poly-G435-DM0lin Chemicals Div.-Olin Mathieson Chemicals Corp. describedas a propoxylated mixture of a-methyl glucoside and 25% glycerine,having a hydroxyl number of 438. Poly G is a registered trademark of theOlin Mathieson Chemical Corp.

Po1y--G560DM-Olin Chemicals Div.0lin Mathieson Chemical Corp. describedas a. propoxylated mixture of 75% :r-methyl glncoside and 25% glycerine,having a hydroxyl number of 556.

Niax Catalyst TMPDA-Union Carbide Chemicals 8: Plastics Dl v. UnionCarbide Corp. N,N,N 'N -tetramethyl-1,B-butane diarnme. Niax is a.registered trademark or the Union Carbide Corp.

DC193Dow Corning Corp.a silicone surfactant described in US. Pat. No.3,402,192. DC is a registered trademark of the Dow Corning Corp.

LVl-23P1\Iichigan Chemicals Corp.-tris(2,3-dibrom0- propyl) phosphate.

Isocyanate component: A quasi-prepolymer having a free NCO content of25.48%, prepared by reacting a large excess of Mondur MR with VeranolP-400 The reactants were mixed at room temperature. The temperature ofthe reaction was thereafter not controlled, and was allowed to followits natural course resulting from the exothermic reaction in a 22 gallonpolyethylene container.

M0ndur MRMobay Chemical Co.-a polymer of diphenyl methane diisocyanatehaving 2-5 isoeyanate groups per molegule. Mondur IS a registeredtrademark of the Mobay Chemical 0. Veranol P400Dow Chemical Co.a linearalpha-omega dihydroxy polypropylene oxide having a molecular weight of400. Voranol is a registered trademark of the Dow Chemical The abovepolyol and isocyanate components at 70 F. and 100 F. respectively werestirred together for 20 seconds, until uniformly blended, in a Weightratio of 47.21 parts polyol to 52.79 parts isocyanate, then immediatelycast onto the treated mold surface. The solution was cast in thin A3")layers, to give an unexpanded polyurethane formulation, in an openshallow flat aluminum mold of /2" x 4" x dimensions in such a mannerthat the upper surface of the castings has been exposed only to air. Thebottom and side surfaces of these castings were formed against the moldwhich had previously been prepared in each of the following ways.

(a) wax mold release only (Partall No. 2 Paste Wax Rexco Chemical Co.-adispersion of solid waxes in an organic solvent).

(b) Polyvinyl alcohol film applied over wax (a) (Partall No. lO-RexcoChemical Co.-a cold water soluble polyvinyl alcohol dissolved at 4%solids in 190 proof ethanol).

(c) Hydroxy propoxy methyl cellulose film applied over wax (a) [Methocel60HG, 50 cp.(Dow Chemical Co.) dissolved in a 50/50 by weightmethanol/water mixture, containing 0.1% of a non-ionic surfactant so asto give a 2% solids content].

The wax used is the same in all of these surfaces. The wetting of thebottom surfaces of these castings molded against mold treatments werecompared against the top (air contact only) surface of the casting whichcould not possibly have been contaminated by the mold surface and/orcoatings.

The surfaces to be tested were designated as follows:

TEST

These castings were tested for wettability by water and energy ofwetting surfaces according to the following tests:

Test IContact Angle The theoretical significance of contact angles andmethods of measuring them are described in Surface Active Agents,Schwartz & Perry, 252-262, (Interscience, 1949). The contact angle is aninverse measure of the wettability of a solid surface by a liquid, withzero degrees representing perfect wetting and 180 degrees no wetting.According to this reference, contact angles of 90 degrees or greaterloosely refer to unwettable surfaces. The contact angles in theseexperiments were measured photographically through a microscope/ mirrorsystem.

Test 11 Another test developed to further differentiate between thewettability of two surfaces consists of spreading a drop of water into a/8" diameter circle and observing whether it remains spread or beads upinto a drop again. A green food dye was incorporated into the distilledwater and photomicrographs taken.

The results of tests I and II are presented in Table I.

TABLE I Contact Work of angle, 0, wetting (1 circle spread Surfacedegrees plus cos 0) test 1 (wax 95. 5 0. 904 Beaded up to drop. 02 (PVAL1 1. 96 Bemained spread. Cs ((Methocel)- 31. 5 1.85 Do. 04 (air) 91 0.980 Beaded up to drop. PVAL fi1m* 28 1. 88 Remained spread.

For comparison, the contact angle of water on a film of the polyvinylalcohol, (PVAL) dried 26 min. at 180 degrees F., is included in thetable.

Test H1 The surfaces C to C were then spray coated with a reactiveZ-component commercial polyurethane paint (Micothane paintexemplified bya mixture comprising 1 part by weight resin RS-350, 2 parts by weightpigment mix 7 8l23 blue and 1 part by weight solvent S816 Midland Div.of the Dexter Corp.) Paint adhesion was measured after 24 hours of roomtemperature drying by the standard cross-hatch tape test, and byscraping the paint with a scalpel blade held perpendicular to thesurface. The results are shown in Table H. (The cross-hatch tape test isa field test commonly used to test adhesion of paint to a substrate;Lines are scribed through the dried paint film with a sharp instrumentat Me" intervals' vertically and horizontally to give a cross-hatchedpattern. The number of squares coming off during crosshatching is ameasure of the degree of adhesion. A piece of Scotch tape is thenadhered to the cross-hatch pattern and pulled off. Again, the loss ofsquares of paint is noted. A very similar test, known as the GeneralElectric test, is described in Principles of Surface Coating Technology,D. H. Parker, 487 (Interscience, 1965).

NorE.Perfect adhesion above is described as follows:

Cross-hatch/tape test.-No removal of paint during scratching of Wcross-hatch pattern in paint coating or during subsequent removal ofScotch tape from cross-hatched coating. Scalpel test.- No separation ofpaint from substrate when scraping through paint Into substrate withscalpel blade.

EXAMPLE 7 This example illustrates a practice of this invention withrespect to molded, cellular polyurethanes. Additionally, this exampledemonstrates (a) the interfacial interaction between a' claimed barrierlayer material and a polyurethane composition in contact with saidbarrier layer applied over a wax, (b) the generation of a polyurethaneplastic surface to which paint strongly adheres and (c) the ability toremove from the polyurethane plastic surface substantially all of thebarrier layer material with water to leave a wax-free and oil-freepolyurethane plastic surface having high wettability and strong paintadhesion in a practice of this invention.

The formulation described in Example 6 was modified by the addition of.monofiuorotrichloromethane to the polyol component of Example 6 suchthat the resulting mixture of the isocyanate component and modifiedpolyol component contained 5.5 parts by weight ofmonofluorotrichloromethane per 100 parts by weight of the total mixture.This addition (to the polyol component) was accompanied by a change inthe weight ratio of polyol to isocyanate components from 47.21/52.79 to50.12/49.88. The latter weight ratio was used in this example. Theaddition of monofluorotrichloromethane did not alter the ratios of theother individual ingredients. The mold described in Example 6 wasmodified by adding a stainless steel liner for the bottom large fiatsurface and an aluminum plate cover. The stainless steel sheet wasdegreased with solvent, washed with an alkaline detergent solution,

1 1 rinsed with distilled water, and air dried. The heated mold wastreated wherein aluminum sides of the mold were waxed, and the aluminumtop cover was Waxed and overcoated with polyvinyl alcohol (using the waxand polyvinyl alcohol described in Example 6), giving surfaces forcomparison with the unaltered surface molded against the stainlesssteel.

115 gms. of the molding composition, prepared at the conditionsdescribed above and in Example 6, was charged to the mold and expanded(foamed) and cured in the closed mold to give the following series oftest surfaces:

M --Molded against a waxed metal mold surface.

M Molded against a polyvinyl alcohol film coated over the waxreleaseagent, subsequently removed from the molding by rinsing with cold water.

M --Molded against thoroughly cleaned stainless steel.

Tests I-II-HI As described in Example 6 tests I and II to measurewettability and test III to measure paint adhesion were conducted onsurfaces M and the results are tabulated below. The painted surfaceswere prepared with the paint described in Example 6, using the proceduredescribed in Example 6.

Work of wetting Contact (1 plus Surface angle, 9 cos 6) circle spreadtest M 71 degrees..- 1. 33 Partially headed up into an elongatedL-shaped drop. M1 (wax) 83 degrees--- 1. 12 Beaded up to drop. Mg (PVAL)17 degrees.-. 1. 956 Remained spread.

No'rE.The stainless steel sheet, upon being separated from the molding,required considerable peel force to separate it from the molding, and anarea of the molding x 3" broke away from the molding and remainedadhered to the stainless steel.

A 2% solution of polyacrylic acid was prepared as follows:

Acrysol A-l (containing 25% polyacrylic acid, 75%

water) (1) 8.00

Water 42.95 Methanol 48.95 Igepal CA-630 0.10

Acrysol A-l: Rohm and Haas C0. polyacrylic acid, less than 50,000molecular wt., 25% in water, pH=2. Viscosity (Brookfield) 15 cp. atcone, 320 cp. at 25% conc. cp.= centipoises. Acrysol is a. registeredtrademark of the Rohm and Haas C0.

Igepal (IA-630: General Aniline and Film 00., octyl phenoxy poly[ethyleneoxy) ethanol containing 9-10 moles ethylene oxide per mole ofhydrophobe. Igepal is a registered trademark of the General Aniline andFilm Co.

The Acrysol A-1 was dissolved in the water at room temperature. Themethanol and the Igepal CA-630 were then added and the solution wosstirred, giving a 2% solution of polyacrylic acid in 50/50water/methanol with .l% wetting agent. A trace of water soluble foodcoloring was added to impart a deep green color to the solution.

A /2" x 4" x cavity aluminum mold was prepared by coating the mold at160 F. with a thin layer of Mitchell-Rand l894EX-5 mold release, whichis a paste dispersion of a mixture of hydrocarbon waxes and estertypewaxes in a hydrocarbon solvent, obtainable from the Mitchell Rand Mfg.Corp. Mitchell-Rand is a registered trademark of the Mitchell-Rand Mfg.Corp. The above paste wax was applied to the mold with a paint brush andwas subsequently reduced to a thin layer by wiping off excess wax with acloth. hTe wax layer was then overcoated with a film of the polyvinylalcohol solution of Example 1, applied to the mold at 150 F. by means ofa spray gun. In the same manner and under the same conditions a clean x4 4" x 10 steel plate was coated with a thin layer of Mitchell-Rand1894EX-5 mold release and then overcoated with a film of the 2%polyacrylic acid solution. The polyacrylic acid solution was thenallowed to dry to a smooth solid film about /2 mil thick.

A polyurethane foaming mixture was prepared as follows:

A-component (isocyanate) A quasi-prepolymer was prepared by slowlyadding at ambient temperature 56 lbs. of Dow Chemical Co. Voranol P-400(polypropylene glycol of molecularv weight about 400) to 444 lbs. ofMoby Chemical Co. Mondur MR (reported to be a polymer of diphenylmethanediisocyanate having 2-5 isocyonate groups per molecule). Theingredients were mixed and allowed to react and stand for 24 hoursbefore analysis and use.

B-component (polyol) 400.0 lbs. of Olin Po1y-G-435-DM (reported to be apropoxylated mixture of a-methyl glucoside and 25% glycerol having ahydroxyl number of about 435), obtainable from the Olin MathiesonChemical Corp.

6.9 lbs. of Dow Corning DC-193, a silicone dispersing agent, obtainablefrom the Dow Corning Corp. (reported to be a copolymer of polydimethylsiloxane and a glycol).

2.8 lbs. of N,N,N',N-tetramethyl-1,3-butane diamine.

68.6 lbs. monofluorotrichloromethane.

103.2 g. of the A-component and 96.8 g. of the B-component were mixed atroom temperature with a high speed propellor agitator and g. of themixture was poured into the cavity of the prepared aluminum mold, now atF. The steel plate at 140 F. whose surface had been treated aspreviously indicated was positioned, treated surface down, over theopening of the mold and then the mold cover placed on top of the steelplate. The mold was closed and clamped shut and the mixture was allowedto react and expand, filling the mold cavity. The mold was then placedin a F. circulating air oven for 20 minutes. After removing the moldfrom the oven, the mold was opened and the molding was removed from themold. The molding released easily from the mold and the steel plate andhad a green color, indicating the polyacrylic acid coating remained onthe molding. None of the green coating was discernible on the cavitysurfaces of the mold or the steel plate. The green coating was easilyremoved by washing the molding with cold running water. Even afterprolonged washing of the molding with Water, the water wet or sheetedout on the surfaces of the molding.

The molding was given a final rinse with a small amount of distilledwater (to prevent hard-water spotting) and allowed to dry. (Next, it waswiped with a clean cloth wet with hexane to remove finger prints orother grease films picked up during handling of the molding.) It wasthen spray-coated with Dexter Corp. (Midland Division) Micothane paint(a two-component reactive polyurethane paint of Example 6). The paintwet the surface of the molding giving a continuous uniform coating about1 mil thick when dried. After air drying the paint and curing it 24hours at room temperature, a test was made to determine the degree ofadhesion between the paint film and the molding surface formed againstthe treated steel plate. The test used, the A3" cross-Scotch tape test,is described in Example 6. No loss of paint was observed during scoringof the cross-hatch pattern, during peeling of the tape from thecross-hatched film, or during a scraping of the cross-hatch with ascalpel blade held perpendicular to the painted surface.

EXAMPLE 9 The procedure of Example 8 was repeated in every detail,except that the coating of polyacrylic acid was omitted and thefollowing solution of polyvinyl pyrrolidone was used in its place.

Antara (General Aniline and Film) polyvinyl pyrrolidone type NP-K3O(40,000 mol. wt.).

Antara is a registered trademark of the General Aniline and Film Corp.2.00 Water 48.95 Methanol 48.95 Igepal CA-630 0.01 Green water solublefood dye Trace The behavior of the polyvinyl pyrrolidone film wasidentical to that of the polyacrylic acid film used in Example 8 in allrespects and the paintability and paint adhesion test results obtainedin accordance with the procedure described in Example 6 wereindistinguishable over those of Example 8 when the molding was paintedas described in Example 8.

EXAMPLE 10 The procedure of Example 9 was repeated in every detailexcept that the 2.00 g. of polyvinyl pyrrolidone in Example 9 wasomitted and replaced by 2.00 g. of Mathieson, Coleman and Bell SolubleStarch, Catalog No. SX 930. Upon spraying the wax-coated steel platewith the starch solution, the starch solution wet the waxed surfacecompletely but somewhat non-uniformly, tending to bead-up slightly.However, after molding the polyurethane molding and removing it from themold, the starch coating remained with the molding and not with thesteel plate and rinsed easily from the molding with cold running water,leaving a smooth molded surface. As in the case of the polyacrylic acidor polyvinyl pyrrolidone coatings, the washed surface was easily wet bywater, which sheeted out on the washed molded surface. Upon painting thedried molding, as described in Example 8 a smooth continuous film ofpaint was obtained. About 810% of the cross-hatched paint pattern wasremoved from the molding during cross-hatching and peeling of the tapein accordance with the test procedure described in Example 6, vs.removal of 100% of the cross hatch pattern from the painted surface ofthe molding of Example 11. The cross-hatched paint scraped off themolded surface with moderate pressure on the scalpel blade.

EXAMPLE 11 For comparison purposes, the procedure of Example 8 wasrepeated in every detail except that no Water soluble coatings wasapplied over the wax coated steel plate before filling the mold withpolyurethane-foaming mixture (i.e. the use of the water soluble barrierlayer was omitted). The polyurethane molding was thus molded directlyagainst the waxed steel surface. The cured molding released easily fromthe mold, but it was noted that water beaded up into tight discretedroplets on the surface, formed against the wax coated steel, even afterattempting to wash the wax from the molded surface with a clean clothwet with hexane. A uniform coating of paint could not be applied to themolding surface formed against the wax coated steel, in accordance withthe painting procedure described in Example 8 because the paint did notcompletely wet the molded surface. Instead, a bubbly, leather-grainpainted surface was obtained. In the crosshatch test conducted inaccordance with the procedure of Example 6, 100% of the paint wasremoved during crosshatching and peeling of the tape, and the paintflaked off easily With only slight pressure while being scraped with ascalpel. This example demonstrates the disadvantages of prior artprocedure for molding polyurethane plastics which require subsequentpainting or other treatments involving adherence to the molded surface.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected Within thespirit and scope of the invention as described above and as defined inthe appended claims.

What is claimed is:

1. A process for producing polyurethane moldings having surfaces free ofadhesion inhibiting mold release agent comprising the steps of:

(a) overcoating a mold, which has been coated with a hydrophobicmold-release agent, with a continuous, solid barrier layer of awater-soluble film forming material reactive with isocyanate groups;

(b) passing into the mold a polyurethane molding composition containingreactive isocyanate groups;

(0) polymerizing said polyurethane molding composition in contact withsaid barrier layer material containing a plurality of moieties reactivewith isocyanate groups;

(d) removing the resultant molding; and

(e) washing the surface of said molding with water to substantiallyremove said Water-soluble barrier layer.

2. The process of claim 1 in which said water-soluble film formingmaterial contains hydroxy groups.

3. The process of claim 1 in which said water-soluble film formingmaterial is polyvinyl alcohol.

4. The process of claim 1 in which said Water-soluble film formingmaterial is a partially hydrolyzed vinyl acetate polymer containingalcohol groups.

5. The process of claim 1 in which said polyurethane molding compositioncontains a blowing agent.

6. The process of claim 1 wherein said water-soluble, film formingmaterial is polyacrylic acid or polymethacrylic acid.

7. The process of claim 1 wherein said water-soluble, film formingmaterial is polyvinyl pyrrolidone.

8. The process of claim 1 wherein said water-soluble, film formingmaterial is hydroxypropylmethyl cellulose.

9. The process of claim 1 wherein said moieties are selected from thegroup consisting of OH, COOH, NH NHR, CONH CONHR and mixtures thereofwherein R is a hydrocarbon radical with 1-12 carbon atoms.

References Cited UNITED STATES PATENTS 3,624,190 11/1971 Cekard, Jr.26454 2,994,111 8/1961 Koss et al. 264338 3,215,763 1l/1965 Buerger264338 3,210,448 10/ 1965 Szabat 26454 3,115,414 12/1963 Lottridge, Ir.10638.25

FOREIGN PATENTS 3,713,872 9/1962 Japan 264338 ROBERT F. WI-HTE, PrimaryExaminer I. B. LOWE, Assistant Examiner US. Cl. X.R.

1. A PROCESS FOR PRODUCING POLYURETHANE MOLDINGS HAVING SURFACES FREE OFADHESION INHIBITING MOLD RELEASE AGENT COMPRISING THE STEPS OF: (A)OVERCOATING A MOLD, WHICH HAS BEEN COATED WITH A HYDROPHOBICMOLD-RELEASE AGENT, WITH A CONTINUOUS, SOLID BARRIER LAYER OF AWATER-SOLUBLE FILM FORMING (b) PASSING INTO THE MOLD A POLYURETHANEMOLDING (B) PASSING INTO THE MOLD A POLYURETHANE MOLDING COMPOSITIONCONTAINING REACTIVE ISOCYANATE GROUPS, (C) POLYMERIZING SAID POLURETHANEMOLDING COMPOSITION IN CONTACT WITH SAID BARRIER LAYER MATERIALCONTAINING A PLURALITY OF MOIETIES REACTIVE WITH ISOCYANATE GROUPS, (D)REMOVING THE RESULTANT MOLDING, AND (E) WASHING THE SURFACE OF SAIDMOLDING WITH WATER TO SUBSTANTIALLY REMOVE SAID WATER-SOLUBLE BARRIERLAYER.